Day Ten

Daniel Berry

(Page 79 of Supporting PCs)

 

Physical or System Memory

 

This lesson will go into the different terms and different types of physical memory on your computer.

Memory

 

Memory addresses

Every program accesses data from RAM by using addresses.  These addresses allow the system to access only the data, which is needed for that specific task.

Data may be stored in four different categories of memory, these are: conventional, UMB, extended, and expanded. 

 

 

Conventional Memory

This memory is used for the DOS OS and any programs, which are loaded in the start-up configuration files.

 

UMBs

Upper Memory Blocks take up the space just above 640KB and take up384 KB.  Device drivers can be loaded in this area.  Win 3.Z and Win 9X use this area to write to a disk or network device.

 

Expanded Memory

This memory area swaps data in and out of conventional memory by using a 64 KB page frame in the upper memory areas.  This page frame is virtual memory; in this case virtual memory is memory that appears larger to an application than it really is, by swapping data on to the hard drive.

 

High Memory

This memory is just above the first 1024 KB of the system memory. It is a small 64 KB portion, which could not be used in older systems due to memory conflicts.  HIMEM.SYS found in DOS 5.0 and above was able to manage this small area.

 

Extended Memory    

This type of memory can only be found in 386 processors and above, unless special software is used.  This is the system memory above the first 1 MB.  Applications, which run within the windows’ environment, can use this memory area.

 

Memory and hardware limitations

The design of the processor determines the amount of memory, which that processor can access. 

 

 

Types of Memory

ROM, RAM, and Video RAM

 

ROM

Read Only Memory, is memory that is “read-only” meaning the system does not write to this memory, it only reads it, like you would read a dictionary.  This memory is nonvolatile, meaning data saved on this memory stays there, even when the power is turned off to the system.  PCs use ROM chips to store important information for the POST, BIOS, which are needed to boot the system.  ROM chips are slower than RAM chips, so the system software copies this data into RAM, to speed things along.  This is called shadowing and can speed up a system. There are four types of read only circuits, these are ROM, PROM, EPROM, and EEPROM.

 

ROM

ROM chips have data or programs on them, which cannot be rewritten or changed, that data is written into the integrated circuits of the chips. This type of read only memory chips are useful when the data or programs, which are written on them rarely change. 

 

Programmable Read Only Memory

These cost more than ROM chips to make, but can be very useful, because they allow a programmer to program data onto the chip.  Once programmed, the chip cannot be re-programmed.

 

Erasable Programmable Read Only Memory

These cost more than PROM chips, but are even of greater value because the data on the chip can be erased and reprogrammed to meet the challenges of new technology. To erase the data on this type of chip, the programmer will open a special window on the chip, expose to UV rays and then install the new data.

 

Electrically Erasable Programmable Read Only Memory

These are the best types of ROM chips because they can be erased and reprogrammed without any special tools.  These are the types of ROM chips, which can be found in today’s machines, allowing them to be reprogrammed to accept newer technology, which was not around when the chip was first made.  The drawbacks are that they have less memory than RAM and can be reprogrammed only so many times before wearing out.

 

RAM

RAM is short for Random Access Memory.  These chip provide an area for the CPU to read and write data.  The data on these chips are volatile, which means that all data stored on these chips is lost when power is turned off.  Both ROM and RAM allow random access of data, but only Ram allows the system to write to the chips.  RAM has two categories, which are Static RAM and Dynamic RAM. RAM speeds are measured in nanoseconds (ns). One nanosecond is a measurement in time, the equivalent of one thousand millionth of a second. You'll see reference to numbers as follows: x-y-y-y within these notes. The "x" refers to the number of clock cycles it takes to read or write the first piece of data of a group of four. Each "y" refers to the number of clock cycles each subsequent piece of data is dealt with in the group. A clock cycle is the speed at which a microprocessor executes instructions. All computers have an internal clock that regulates the rate at which instructions are executed.  Clock speeds are measured in megahertz (MHz). One MHz is equal to one million cycles per second. SIMM and DIMM: Both are simply the packaging types that RAM comes in. SIMM stands for Single In-line Memory Module and DIMM stands for Dual In-line Memory Module. SIMMs have to be installed in pairs. For example, if you have eight RAM slots in your motherboard then you have to add them two at a time. You couldn't install seven SIMMs and leave one slot empty. A DIMM can be installed one at a time. Then there's parity and non-parity RAM. You can tell if your RAM module has parity checking by counting the number of chips on it. If the count is odd, you have parity checking.

 

Static RAM

These chips have sets of four to six transistors.  They have a complex design, which allow them to be very fast, but expensive.  This type of RAM is found in the system’s cache memory. There are several types of SRAM: Static RAM: This type of RAM is mostly used for Level 2 Cache, Async SRAM (Asynchronous Static RAM), Sync SRAM (Synchronous Burst Static RAM), and PB SRAM (Pipelined Burst Static RAM)

 

Async SRAM (Asynchronous Static RAM)

This type of SRAM has been used for years, ever since the first 386 with L2 cache came out. It comes in 20, 15 or 12ns speeds, but it is not fast enough to be accessed synchronously. The amount of time the CPU has to wait for this RAM is only a little bit shorter than for DRAM.

 

Sync SRAM (Synchronous Burst Static RAM)

This type of SRAM delivers data in 2-1-1-1 burst cycles only up to the 66 MHz border. As soon as that border is crossed it slows down to 3-2-2-2 bursts. Sync SRAM is not supported in the newer Pentium boards and is slowly becoming expensive as fewer companies manufacture it. It comes in speeds of 12 - 8.5ns.

 

PB SRAM (Pipelined Burst Static RAM)

This is the most popular cache RAM of all. It is the fastest for bus speeds of 75 to 133MHz. It can deliver burst speeds of 3-1-1-1 regardless of processor clock speed.

 

Today’s SRAM

With the every growing speed of the CPU, the speed of it’s memory systems, and buses become far more important than in the past.  With CPU speeds of above one GHz, the systems L1 and L2 caches must be at least half of the CPU’s speed, as to not slow down the processor.   The P-III Coppermine has L2 cache built into the CPU itself, allowing for the fastest transfer of data between the CPU and L2 cache.   

 

Dynamic RAM

These chips have sets of one transistor and one capacitor.  They have a simple design, which lowers costs and allows them to hold higher memory densities than SRAM, but are slower.  DRAM has had many improvements over the years.  The following is a list of these improvements.

 

FPM DRAM

This is Fast Page Mode DRAM.  It allows the row address to be sent only once if multiple columns on a row must be written or read. This RAM has been around for years. It comes in speeds of 70ns and 60ns. The 70ns type is used in older systems, and 60ns is used in systems equipped with the Pentium 100, 133, 166, 200 MHz. Fastest access speeds in CPU cycles are 5-3-3-3 in burst reads.

 

EDO DRAM

This is Extended Data Out DRAM.  It allows for the next read or write to start before the previous one finishes.  This is about 3 to 5 percent faster than FPM DRAM.  EDO RAM is limited to bus speeds below 66 MHz.  EDO comes in 70ns, 60ns, and 50ns speeds, and should be used with most Pentium 100 to 200 MHz systems. It can pump data out in less clock cycles that FPM RAM. If you need to buy EDO RAM for an older Pentium system, then aim for the 60ns or preferably the 50ns speeds.

 

BEDO DRAM

This is Burst extended data out DRAM.  These chips combine EDO technology with pipeline burst capabilities to improve performance.  This RAM is an improvement over EDO. The CPU is able to read data in a 5-1-1-1 burst. As with EDO, BEDO cannot handle bus speeds over 66 MHz. BEDO is only supported by a few chipsets: VIA 580VP, 590VP, 680VP.  VIA 580VP and 590VP are used with Intel Pentiums and the Cyrix 6x86. The 680VP chipset is used in the Pentium Pro.

 

SDRAM

This is Synchronous DRAM.  This technology improved the speed of RAM tremendously and can work with bus speed of above 133 MHz. Its access speed is 5-1-1-1, the same as BEDO RAM. SDRAM has become very popular since it was supported by the Intel Triton VX, and BX chipsets along with all new VIA chipsets.

 

RAMBus DRAM (RDRAM)

PC100 SDRAM’s bandwidth is (100 MHz Operating Speed) x (64-bit Bus) x (1/8 bytes per bit) = 800 MB/s available bandwidth.  PC100 SDRAM’s bandwidth is (133 MHz Operating Speed) x (64-bit Bus) x (1/8 bits per byte) = 1066 MB/s available bandwidth.  RDRAM sets up like this: (400MHz Operating Speed) x (16-bit Bus) x (2 Rising & Falling Edge) / (8 bits per byte) = 1600MB/s available bandwidth.

DDR SDRAM

Double Data Rate SDRAM is little more than a small evolution of current SDRAM technology. DDR SDRAM is capable, like RDRAM, of transferring data on both the rising and falling edges of the clock cycle. As such, its effective bandwidth is doubled. Consider standard 100 MHz DDR SDRAM:  At 100 MHz (100 MHz Operating Speed) x (2x Rising & Falling) x (64-bit Bus) / (8 bits per byte) = 1600 MB/s available bandwidth, at 133 MHz (133 MHz Operating Speed) x (2x Rising & Falling) x (64-bit Bus) / (8 bits per byte) = 2133 MB/s available bandwidth. 

 

Video RAM

This type of RAM is used in video cards.  There are at least 8 types of video RAM, these are DDR RAM, VRAM, WRAM, SGRAM, MDRAM, FPM, and EDO RAM.

 

   FPM and EDO

These types of memory chips were used in older, slower video cards.  Avoid buying video cards with this type of memory installed.

 

Video RAM (VRAM)

A 100% improvement over EDO RAM.  This RAM can send data to the monitor and receive data from the CPU at the same time.

 

Window RAM (WRAM)

A 25% improvement over VRAM.  It is less expensive than VRAM to produce and therefore has lowered the cost of video cards using this RAM.

 

Synchronous Graphics RAM (SGRAM)

SGRAM uses similar technology as EDO RAM, but is many times faster, this allows the performance of VRAM, but at a fraction of the cost, again lowering costs!

 

Multibank DRAM (MDRAM)

MDRAM uses newer technology to achieve performance similar to WRAM, but at lower cost.

 

DDR SDRAM

This is the fastest memory type available.  On video cards DDR can operate above 300 MHz to deliver outstanding bandwidths!  This is the type of RAM, which is used in the new GPU (Graphic Processing Unit) of the nVidia - GeForce 2.  What is a good amount of RAM to installed on your next video card?  32 Megs is the lower limit and recommended for non-hard-core-gamers, 64 is nice and will allow larger worlds to be stored into the video card for a more realistic virtual world experience.  128 Megs on the video card should only be considered if you are a hard-core-gamer!  The Creative Labs nVidia TNT2 with 32 Megs is a perfect buy for the average user.  The Creative Labs nVidia GeForce 2 with 32 or 64 Megs is what gamers and users who use large graphic files should look into.

 

Controlling memory Errors

There are parity, non-parity, and ECC methods used to control errors.

 

Non-Parity

This is RAM without any control over errors.  It assumes that all data is correct 100% of the time.  It is cheaper than parity RAM.

 

Parity

This error correcting Ram uses an extra bit added to each byte of RAM to verify the accuracy of the bytes stored in memory.

 

ECC

This is Error correcting Code RAM, which can detect 2 bit errors, correct them and continue working without slowing down.  ECC RAM is used in P-II and above systems.

 

RAM Configurations

There are three configurations for RAM.  These are: Dual-in-Line Package (DIP), Single-in-Line Memory Modules (SIMM), and Dual-in-Line Memory Modules (DIMM).

 

DIP

These chips have two rows of prongs that fit into a special socket.  It is rare to ever see this RAM.

 

SIMM

These have many chips soldered onto a single module.  There are 30 pin and 72 pin SIMMs.  Normally two SIMMs are needed in order to complete one bank of memory.  The RAM sizes of SIMMs is 4, 8, 16, 32, 64, and 128 Megs.

 

DIMM

These have many chips soldered onto a single module like SIMMs, but are larger and have both sides of the module in use.  There is a 168 pin DIMM in use for P-II~ III systems.  The RAM sizes of DIMMs is 16, 32, 64, 128, 256, and 512 Megs.

 

 

 

 

 

By the way, the Celeron use a 66MHz bus speed (unless overclocked) and have 128K of cache at processor speed. The PIII (old) has 512 of 1/2 speed cache. The newer PIII “coppermine” has 256 of full speed cache, and is better optimized than the Celeron cache, so it is faster, as well as the 100 or 133 bus/memory speed. OH, the new Celeron II has the SIMD instructions, but it would take an 850MHz Celeron II to be as fast as a PIII 600, because of the cache and bus speed issues. The Celeron certainly has a FPU (math unit) onboard, but the new Athlon/Duron has an even better FPU at a much lower cost.

 

RAM

 

Soft memory errors are caused by____

a) Bad Simm

b) Short in circuit

c) Random events

 

"Parity" errors usually indicate bad memory.

a) True

b) False

 

A parity error usually indicates a problem with:

a) memory

b) hard drive

c) hard drive controller

d) i/o controller

e) power supply

 

What action will enable more applications to run simultaneously?

a) Add larger hard drive

b) Increase size of Pagefile

c) Upgrade CPU

d) Add RAM

 

Which provides the fastest data access time?

a) RAM

b) ROM

c) CD-ROM

d) Hard disk

e) Floppy disk

 

What component would most likely cause a "parity error"?

a) Hard disk

b) Controller

c) Bad RAM

d) Software

 

Which provides the fastest data access time?

a) RAM

b) ROM

c) CD-ROM

d) Hard disk

e) SCSI hard drive

 

What component is most likely to cause a "parity error"?

a) Hard disk

b) controller

c) Bad RAM

d) Software