Systems Design and Programming DMA I CMPE 310 Disk Memory Systems Magnetic and optical: • Floppy disks • Hard disks • CD-ROMs and WORMs (write once/read mostly) • DVD Floppy: Sector Outter track Commonly hold between 512 to 1024 bytes of data. Inner track L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 1 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Floppy Older 5 and 1/4 flexable floppies spin at 300 RPM, have 40 tracks with 9 sec- tors/track and two sides. Capacity = 40 X 2 X 9 X 512 = 368,640 or ~360K bytes of information. Newer ones are high-density with 80 tracks and 15 sector/track for 1.2 MB. Heads actually contact the disk surface, leading to wear out. The recording format called MFM (modified frequency modulation) used to write double density format. 1 0 0 1 0 1 1 C D C D C D C D C D C D C D L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 2 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Floppy The rules are given as follows: A data pulse is always stored for a logic 1. No data and no clock is stored for the first logic 0 in a string of logic 0s. The second and subsequent logic 0s in a row contain a clock pulse, but no data pulse. The clock is inserted in subsequent 0s to maintain synchronization as data is read from the disk. The micro-fl oppy is much mor e popular today: Write protect Head door Head slot L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 3 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Floppy Advantages of the micro-fl oppy over the mini-fl oppy . Rigid plastic case provided better protection. Head door kept disk from being exposed. Write protection mechanism. Keyed mechansim for track 0. Increase in storage capacity: 80 tracks X 2 sides X 18 sectors/track X 512 bytes/sector = 1.44 MB. Extended high density micro-fl oppy capable of 2.88 MB. A second extension is the fl optical disk which stores data magnetically using an optical tracking system. It stores 21 MB of data. Hard Disks: Use a fl ying head to stor e and read data from the platters and spins at 3,000 to 10,000 RPM (> 10X that of fl oppies). L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 4 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Hard Disks Hard disks usually have at least 4 platters and can have 2 heads per surface. cylinder Stepper motor or platter voice coil track surface sector head The heads are moved from cylinder to cylinder using a voice coil. Hard disks use MFM or RLL (run-length limited) to store information. RLL 2,7 is common today -- this indicates that the number of zeros in a row is always between 2 and 7. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 5 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Hard Disks The data is first encoded using the table given below. Note that this encoding always guarantees at least 2 zeros and no more than 7 zeros in a row. Input Data Stream RLL output 000 000100 10 0100 010 100100 0010 00100100 11 1000 011 001000 0011 00001000 This encoding allows nearly a 50% increase in storage capacity over MFMs without changing the driver electronics or disk surface. RLL drives increase the number of tracks from 18 to 27 to achieve this. 40 MB -> 60 MB with better performance. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 6 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Hard Disks For example, given the data stream 101001011: 1 0 1 0 0 1 0 1 1 MFM RLL 010 001 001 001 001 000 Although all disks use MFM or RLL, disk interfaces vary. Todays systems use ESDI (non-existent), SCSI (small computer system interface) and IDE (integrated drive electronics). IDE incorporates the disk controller in the disk drive and usually contain a 32 KB cache. Access times are less than 10ms (compared with 200ms for fl oppies). L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 7 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Optical Disks CD-ROM land pit Transparent, protective layer Lenses Laser Lenses Photodiode CD-ROMs and WORMs store up to 660 MB of data. DVDs are similar but have much higher bit density (4.7, 8.5 and 17 GB). L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 8 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Video Displays Color displays are extremely popular. Some accept informaton as a composite video signal (similar to TVs), as TTL voltage level signals (0 or 5V) and as analog signals (0 to 0.7V). Composites are disappearing since high-resolution cannot be achieved. They combine the color information with other information such as sync pulses. Most modern systems use direct vido signals with separate sync signals. Monochrome monitors use one wire for video, one for horizontal sync and one for vertical sync. Color monitors use three video signals, one for red, green and blue (RGB). The TTL RGB Monitor: It uses TTL level signs (0 or 5V) as video inputs and a 4th line called intensity. It can display a total of 16 different colors (CGA in older systems). L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 9 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 TTL RGB Monitor The following table gives the RGB values and colors: Intensity Red Green Blue Color 0 0 0 0 Black 0 0 0 1 Blue 0 0 1 0 Green 0 0 1 1 Cyan 0 1 0 0 Red 0 1 0 1 Magenta 0 1 1 0 Brown 0 1 1 1 White 1 0 0 0 Gray 1 0 0 1 Bright Blue 1 0 1 0 Bright Green 1 0 1 1 Bright Cyan 1 1 0 0 Bright Red 1 1 0 1 Bright Magenta 1 1 1 0 Yellow 1 1 1 1 Bright White Cyan is a combination of Green and Blue, Magenta - Red and Blue, etc. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 10 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 TTL and Analog RGB Monitor The connector pin definitions for either color or monochrome 1 and 2: Ground 6: Intensity 3: Red video 7: Normal video 4: Green video 8: Horizontal retrace 59 4 8 3 7 6 2 1 5: Blue video 9: Vertical retrace Horizontal and vertical retrace are for synchronization. Normal video is used for “intensity” on monochrome monitors. Analog RGB Monitors Analog RGB monitors have 3 video signals (no intensity) that can be driven with values between 0 and 0.7 V. Most can display 256K, 16M or 24M colors. 10 and 15: GND 1: Red 11: Color detect (GND mono) 2: Green (mono) 3: Blue 12: Mono detect (GND color) 8157146 13 12 11 10 9 4 and 5: GND 13: Horz sync 5 4 3 2 1 6/7/8: RGB GND 14: Vert sync 9: Female is blocked 15: GND L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 11 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Analog RGB Monitor Most analog displays use a DAC to generate each color video voltage. A common standard uses a 6-bit DAC for each video signal for 64 dis- tinct voltage levels over 0 to 0.7 V range. 64 X 64 X 64 = 262,144 (256K) colors. 8-bit DACs yield 16M colors. Conversion time between 25ns and 40ns is required of the DAC. The next slide shows the video generation circuit used in VGA systems. Each color is generated with a 18-bit digital code (6 each for RG &B). A high speed palette SRAM (access < 40ns) is used to store 256 different 18-bit color codes (hardware colormap) out of the 256K possible (2 18 ). The 8-bit values (8 bit depth) in the video display RAM specify one of the 256 colors for each pixel position on the screen. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 12 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Systems Design and Programming DMA I CMPE 310 Analog RGB Monitor U1 U4 8 Q 0 1Y1 1A1 D 0 6 ... ... ... ... D 5 Q 5 2Y4 2A4 VGA OC Clk 2G 1G circuit U2 U5 6 Q 0 D 0 1Y1 1A1 ... ... ... ... D 5 Q 5 2Y4 2A4 OC Clk 2G 1G U3 U6 Q 0 D 0 6 DAC Q 0 1Y1 1A1 D 0 ... ... ... ... ... ... D 5 Q 5 D 5 Q 5 2Y4 2A4 OC Clk OC Clk 2G 1G Q 0 D 0 O1 RTC I1 U10 A 0 D 0 DAC S0 O2 ... ... I2 D 0 Q 0 D 5 Q 5 S1 I3 O3 ... ... ... ... S2 Q 5 OC Clk I4 D 5 A 7 D 17 O4 18 16R8 I5 OC Clk WR O5 CS I6 O6 Q 0 D 0 I7 O7 OE DAC ... ... I8 WE O8 25 D 5 Q 5 Clk MHz 256x18 OC Clk OE Palette RAM L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 13 (May 5, 2002) I E S R C E O V U I N N U T Y 1 6 9 6
Recommend
More recommend
