Memory Hierarchy Registers Cache Main Memory Fixed Disk (virtual memory) Tape Floppy Zip CD-ROM CD-RWR Cost/Bit Access/Speed Capacity

Connection of memory to the Processor MAR MDR Memory Up to 2k addressable locations Word length = n bits K-bit address bus N-bit data bus Control lines R/W’, IRQ,IE, etc…

Address/Data Connections MEMMEM Data[N-1:0] Address[log2(K)-1:0] K x N K locations, N bits per location Address bus has log2(K) address lines, data bus has N data lines. Address pins labeled A n-1 – A 0 where A 0 is least significant Data pins labeled D n-1 – D 0 where D 0 is least significant

Memory Chips Most devices are 8-bits wide (Byte- addressable); some are 16-bits, others 1 bit wide. Listing refer to memory locations x bits/location –1Kx8, 16Kx8 Often classified by total bit capacity –1Kx8 (8K device) –64Kx4 (256K device)

Control Connections MEMMEM Data[N-1:0] Address[log2(K)-1:0] CS OE WE Chip Select – must be asserted before Memory will respond to read or write operation. If negated, data bus is high impedance. May have more than one – if so, all must be asserted. OE – Asserted for read operation, Memory will drive data lines. WE – Asserted for a write operation (Memory inputs data from data pins, processor writes to memory). There may only be one control line (R/W)

Can see use of CS, W and OE signals. Pentium Memory System – 4G capacity 64 bit data bus, 32 bit Address Bus

Main Memory Characteristics Semiconductor Chips  Housed in DIP Packages  DIP Packages Mounted on SIMM, DIMM Circuit Boards Characteristics  Access Times(read,write,erase)  Faster is Better (varies from minutes to a few ns)  Volatility  Ability to Retain Data After Power is Removed  Power Consumption  Less is Better (mW to nW typical)  Density  Larger is Better (bits/sq. micron or transistors/bit)  Cost  Less is Better

Three Basic Types of RAM RAM – Random Access Memory –memory that can be both read and written during normal operation. –Contents are non-volatile, will be lost on power off. Dynamic RAM Must be refreshed within less than a millisecond Most main memory is dynamic RAM (least expensive) –FPO Fast Page Mode – Can only match speed of 30MHz data bus –EDO Extended Data Out – 66MHz motherboards or less –BEDO – burst enhanced data-out – –SDRAM – Synchronous dynamic – operates synchronously with system clock and data bus. Can handle 100MHz or more –DDR – Double Data Rate – can transmit data on both edges of the clock –RD – Rambus – operates in a serial fashion rather than parallel

Static RAM Fastest access time of memory types. Typically the type of RAM used primarily in Level -2 cache. Read, Write operations take equal amounts of time. Access to any ‘random’ location takes same amount of time. Basic memory cell is a latch, takes 6 transistors per memory bit.  SRAM –static - high speed memory that does not require a refresh operation. Much faster than dynamic RAM, with speeds between 8-12 nsec. PBSRAM – pipeline burst - static RAM that has been enhanced by the use of burst technology. Multiple requests can be collected together and sent as a single pipelined request. Bus speeds of 75MHz or higher.

Static RAM Cell

Video RAM VRAM – dual ported, allowing one port to continuously refresh the display while the other port writes data to the display. Results in lower eye strain than possible with DRAM. WRAM windows RAM – optimized for graphics displays using Windows. Can refresh screen more quickly than VRAM SGRAM – synchronous graphics RAM – single ported RAM used on accelerator cards. Two memory pages can be open at the same time. Able to clear memory very quickly. 3D graphics.

ROM ROM – Read Only Memory - a type of memory that cannot be written, can only be read. Contents determined a manufacture time. –ROM is non-volatile – contents remain even when power is off. PROM – Programmable ROM – a type of memory whose contents can be programmed by the user –OTP – One Time Programmable, a PROM is OTP if contents can be programmed only once. EEPROM – Electrically Eraseable PROM – contents be erased electrically by the user. –Memory is not alterable under ‘normal’ operation.

4x5 PROM Organization 1-Bit Storage Cell

SIMMS and DIMMS Mount Memory Device Packages on Circuit Boards to Conserve Space 30-Pin SIMM – First – Single Byte Access Used in “Pairs” Since in x86 1 Word=16 bits 72-Pin SIMM – Four Byte (32 bit) Access Need Pairs for Pentium+ Since 64 bit Data Bus 168-pin DIMM – Eight Byte (64 bit) Access SIMM – Single In-Line Memory Module DIMM – Dual In-Line Memory Module

8M x 32 (32MB) SIMM

Flash Memory Hybrid of RAM/ROM Have basically replaced EEPROMs Memory parts can be electrically erased and reprogrammed without removing the chip. The entire chip (or block) must be erased at one time. Individual byte erasure is not possible. Silicon Hard Disks – PCMCIA (Personal Computer Memory Card International Association) – credit card size ROM BIOS, Font cards for printers, automotive industry diagnostic codes, modems, Ethernet cards

Semiconductor Memory Device Architecture 2  4 Decoder A1A1 A0A0 D3D3 D2D2 D1D1 D0D0 D4D4 Storage Cell Array Buffers

DECODER REVIEW n×2 n Device – n encoded inputs – 2 n decoded outputs 2  4 Decoder A1A1 A0A0 D3D3 D2D2 D1D1 D0D0 A1A1 A0A0 D3D3 D2D2 D1D1 D0D

Buffers Differential Amplifier – Gain:A v – 2 input voltages, 1 output voltage referenced to common ground V in V out = A v V in AvAv Single-Ended Amplifier – Gain:A v – 1 input voltage, 1 output voltage referenced to common ground V1V1 V out = A v (V 1 -V 2 ) AvAv V2V2 + -