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1 Computers Internal and External Memory. 2 Characteristics of Computer Memory zLocation zCapacity zUnit of transfer zAccess Method zPerformance zPhysical.

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Presentation on theme: "1 Computers Internal and External Memory. 2 Characteristics of Computer Memory zLocation zCapacity zUnit of transfer zAccess Method zPerformance zPhysical."— Presentation transcript:

1 1 Computers Internal and External Memory

2 2 Characteristics of Computer Memory zLocation zCapacity zUnit of transfer zAccess Method zPerformance zPhysical Type zOrganization

3 3 UNIVAC Console and CPU

4 4 CPU’s

5 5 Memory Hierarchy CACHE MAIN MEMORY MAGNETIC DISK | DISK CACHE MAGNETIC TAPE | OPTICAL DISK SPEEDCOST REGISTERS

6 6 Capacity Units zBit zByte zKilobyte zMegabyte zGigabyte zTerabyte zb zB = 8 b zKB = 1,000 B zMB = 1,000,000 B zGB = 1,000,000,000 B zTB = 1,000,000,000,000 B

7 7 Memory Access Method zSequential - tape zDirect - floppy or hard disk zRandom - internal memory yDynamic (DRAM) simple, small, must be refreshed yStatic (SRAM) no refresh needed zAssociative - some cache

8 8 Random Access Memory zChips and chip technology

9 9 Flip Flop Circuit Diagram

10 10 Memory Cells 0/1 SELECT select cell CONTROL read or write DATA IN / SENSE input or output SELECT select cell CONTROL read or write 1

11 11 Write to Memory COL ADDRESS BUFFER MUX REFRESH ARRAY DATA INPUT BUFFER DATA OUTPUT BUFFER A0. A10 D1. D4 ROW ADDRESS BUFFER Read Enable Col Address Row Address Write Enable Row Address ROW ADDRESS BUFFER COL ADDRESS BUFFER Col Address MUX Write Enable DATA INPUT BUFFER

12 12 Pin Assignments zA0 … A10: address location (multiplexed) zD1 … D4: data in or out zVcc: power supply zVss: ground zRAS: row address select zCAS: column address select zWE: write enable zOS: output enable

13 13 Cache Operation ALUCNTL..... BUS MAIN MEMORY CACHE

14 14

15 15 Cache Main Memory CPU CACHE Word Block

16 16 Cache

17 17 Random Access zDirect Access Storage Device (DASD) or disk drives yOptical yMagnetic

18 18 Optical Disks (CD’s)

19 19 How CD’s work

20 20 Cylinder/Track/Block Block (Sector)Track Cylinder

21 21 Disk Organization

22 22 DASD Structure Read-Write Heads

23 23 Data Storage zFAT (File Access Tables), Directories and Catalogs zUpdate and Delete zFragmentation and reorganization zBlocks, Headers and Interblock Gaps

24 24 DASD Access (PC) MAIN MEMORY DASD BUFFER CONTROLLER CPU CACHE

25 25

26 26 DASD Access (PC) MAIN MEMORY DASD BUFFER CONTROLLER CPU

27 27 DASD Access (Mainframe) MAIN MEMORY DASD BUFFER CONTROLLER CPU CHANNEL

28 28 Data Structure HEADERDATACRCHEADER BLOCK Header written when disk is formatted Data copied into block Cyclical Redundancy Check calculated

29 29 Controller Operation (DASD retrieval) zCPU passes parameters to registers in the controller zThe controller transfers data into the card buffer zThe controller checks the CRC to assure the data was copied correctly zThe controller (or CPU) transfers buffered data to memory one word at a time

30 30 Access Time: time from call until first data available zDisk Access Time = Rotational Delay + Seek Time + Transfer Time zRAM Access Time = yRefresh Time + Transfer Time

31 31 Access Time Example zDisk Drive has y7200 rpm = 120 rps y8 ms average seek time y80 MBps transfer rate zRotational delay = 1/2*1/120 = 1/240 s =.0042 zSeek Time = 8/1,000 s =.0080 zTransfer Time = 512/80,000 s =.0064

32 32 Time Units zMillisecond zMicrosecond zNanosecond zPicosecond zms = 1/1000 s zµs = 1/1,000,000 s zns = 1/1,000,000,000 s zps = 1/1,000,000,000,000 s

33 33 Representative Times zNetwork speed = megabits per second zDisk transfer = megabytes per second zDisk access = milliseconds zMemory access = nanoseconds zMachine cycle = microseconds/nanoseconds

34 34 Error Correction and Checking Add bits to a block to use for error discovery yDetection only yDetection and retransmission yDetection and recovery CheckBodyHeader Block

35 35 Error Detection Only (Asynchronous Transmission) ************** Parity Bit 7 Data Bits 2 7 = 128 distinct characters *

36 36 Error Detection &Correction (Hamming Code: 4 bit word) ******** 3 Error Checking Bits 4 Data Bits ******

37 37 DATA Error Detection &Correction (Hamming Code: 4 bit word) ******

38 38 PARITY (even) Error Detection

39 39 PARITY (even) Error Correction (4 bit word)

40 40 Error Correction & Detection zError detection takes fewer bits than error correction zLonger packets take a smaller percent for correction but have more types of errors zHamming’s scheme detects all errors at a high overhead cost; others may correct only single bit or double bit errors with shorter check fields

41 41 CRC Error Checking zThe transmitted messages are divided into predetermined blocks zThe blocks are divided by a fixed divisor zThe remainder is appended to the message

42 42 IBM 1107 with tape drives

43 43 Memory


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