Hardware Fundamentals

Flashcards covering the lecture notes on Hardware memory and error correction.

Memory

Internal storage areas in the computer that comes in the form of chips.

Volatile

Data/information is lost when power is turned off.

Non-Volatile

Data/information is retained when power is turned off

Random Access

Data/Information can be accessed in any order at any time.

Sequential Access

Data/information must be accessed one after the other in a chronological fashion.

Random Access Memory (RAM)

Random access, volatile, read and write memory.

Read Only Memory (ROM)

Random access, non-volatile, read and write memory.

Speed of RAM

How long it takes to retrieve data from memory, usually measured in nanoseconds (ns).

Price of RAM

How much the memory costs.

Static RAM (SRAM)

Cache and Registers.

Dynamic RAM (DRAM)

SIMMs and DIMMs.

Dynamic RAM (DRAM)

1 transistor plus 1 capacitor represent each bit

Dynamic RAM (DRAM) Uses

Main memory. Cannot hold the electrical charges that represent bits forever - they need to be refreshed every 2ms (500 times a second) or the data stored is lost.

Video RAM (VRAM)

A special type of DRAM used in video cards where the CPU can write data to VRAM at the same time the video card's processors read data from VRAM. It also has double the bus width of standard DRAM.

Static RAM (SRAM)

4-6 transistors are used to represent each bit. Each transistor is a small switch. 1's and O's are represented by having different switches turned on or off.

Static RAM (SRAM) uses

Cache and CPU registers. It's a type of DRAM, so it needs to be refreshed every 2ms.

SRAM Characteristic

Special high speed memory (buffer (holding area)).

Cache

Not so much a type of memory but a use of memory to speed up access to data used to hold commonly accessed data.

Hardware Cache

Uses special memory chips to hold data (i.e. L1, L2 and L3 cache).

Software Cache

Uses the computers RAM to store data where special software is used to manage a software cache.

Hardware Cache

Built right into the hardware using special memory chips and special circuitry (SRAM). These purpose designed circuits allow data to be transferred quickly, and the special memory works quickly too.

Level 1 cache (L1 cache)

Located on the CPU chip and built into the CPU design accessed via the CPU’s internal bus. Fastest and most expensive type of cache usually present in small amounts.

Level 2 cache (L2 cache)

Located on the CPU and accessed using the same system bus that the main memory (RAM) uses or the internal CPU bus. Slower than L1 cache but faster than L3 cache. Cheaper than L1 cache but still more expensive than main memory present in larger amounts than L1 cache but smaller than L3 cache

L3 cache

Found outside older CPUs, but on the actual chip in newer CPUs. Faster than main memory but slower than L1 and L2 cache. Still more expensive than main memory Present in larger amounts than L1 and L2 cache, typically in MB.

DRAM characteristics

Slower than SRAM, cheaper to buy per GB, used in main memory (i.e. SIMM/DIMM), more compact, less power and requires refreshing approximately every 2ms (500 times a second) or the data stored is lost due to the DRAM not being able to hold the electrical charge that represents the bits forever

DRAM

1 transistor plus 1 capacitor represent each bit where the capacitor can hold an electric charge.

Fast page RAM (FPRAM)

Traditional DRAM with an access time of 50ns - 80ns.

Extended data out RAM (EDO RAM)

Can send data even while it is receiving instructions about what to do next and is 20% faster than FPRAM

SDR Synchronous DRAM (SDRAM)

Has two banks of transistors for storing data where one bank can get ready for accessing data while the other bank is actually accessing data and is 20-35% faster than EDO RAM

30-pin SIMM

Single Inline Memory Module. Fast Page Mode RAM (FPMRAM). Traditional DRAM. 50ns-80ns. 9 chips in a row/line – one chip is used for parity. Older, used in 386 – 486. 8 bits wide.

72 pin SIMM

Extended Data Out RAM (EDORAM). Send data while receiving instructions about what to do next and is 20% faster than FPMRAM. 8 chips in a row/line – there is no parity chip. Used in 486 and early Pentiums. 32 bits wide.

168 pin DIMM

SDR SDRAM (Synchronous DRAM). Two banks of transistors for storing data (i.e. one bank can get ready for accessing data while the other bank is actually accessing data). 20-35% faster than EDO RAM. 1 transfer per clock cycle. Used in Pentium, Pentium MMX, Pentium Pro, Pentium II, Celeron, Pentium III and Pentium 4. 64 bits wide.

184 pin DDR1 SDRAM

2 transfers per clock cycle. Twice the data transfer rate of SDR SDRAM. 64-bits wide although supports dual-channel, effectively providing a 128-bit data path. Slower than DDR2 SDRAM but faster than SDR SDRAM. Varying speeds - 200, 266, 333, 400MHz are common. Used from Pentium 4

240 pin DDR2 SDRAM

2 transfers per clock cycle. 64-bits wide although supports dual-channel, effectively providing a 128-bit data path. Faster than DDR1 SDRAM. Again, varying speeds - 400, 533, 667, 800, 1066MHz. Also used from Pentium 2, but spans a longer time than DDR1 SDRAM

240 pin DDR3 SDRAM

2 transfers per clock cycle. 64-bits wide although supports dual, triple and quad- channel. Up to twice as fast as DDR2 SDRAM. Low operating voltage. Again, varying speeds – 800, 1066, 1333, 1600, 1866, 2133MHz Used from 2007 onwards

288 pin DDR4 SDRAM

Increased speed. 2 transfers per clock cycle. Lower operating voltage. 64-bits wide although supports dual, triple and quad- channel. Minimum speed 2133MHz (?) – compare DDR3 SDRAM. Again, varying speeds – 2133, 2400, 2666, 2800, 3000, 3200, 3600MHz Used from 2014 onwards

Mask ROM

Programmed by manufacturer with photographic mask of desired bit pattern (data). Cheap only in large quantities (upwards of 10,000 made at once). Used for BIOS on keyboard

PROM

Programmable ROM which is programmable once only by user. Most common type = fuse link PROM. Microscopic internal fuses are selectively burnt / blown by applying 35 volts. Once a fuse is burnt it cannot be rejoined. Used for BIOS on NIC

EPROM

Erasable PROM with a clear Round quartz window in top of chip. Shine UV light onto chip to erase data can be repeatedly erased and reprogrammed in an EPROM burner Window covered with sticker to prevent long term accidental erasure Used for BIOS on motherboard, BIOS on NIC, BIOS for video cards

EEPROM or EAROM

Electrically EPROM or Electrically Alterable ROM which is aka Flash ROM. can be reprogrammed in-circuit (like RAM). Used to store infrequently changing data. write time is much slower than read time. Advantage – can upgrade the BIOS via FDD or Internet download Disadvantage – Can be reprogrammed by a virus (susceptible to BIOS virus). Used for BIOS on motherboard, BIOS on NIC, BIOS on video cards, TV, VCR, Stereo presets

BIOS

The basic input/output system or BIOS connects the computer to its keyboard, monitor and hard drives. During start up, the BIOS controls the boot process.

Error Detection and/or Correction RAM

Error correction used to identify when errors have occurred and where possible, correct those errors so that we still get the original data that was stored, despite the error having occurred.

Parity Checking

Each byte will have a odd number of ones in it. The ninth bit, called the parity bit, is set to 1 or 0 to make sure that there is an odd number of bits.

Error Correction Code (ECC) RAM

A memory system that tests for and corrects errors automatically, very often without the operating system being aware of it, let alone the user.