Computer Foundations Dr. John P. Abraham Professor UTPA

Data Organization Binary Decimal Hexadecimal Translated into: –ASCII –Unicode –EBCDIC

Data Sizes Bit, byte, word, block Big endian (Apple using Motorola), – = Little endian (machines using Intel Pentium) – =

Data structures Computers know the layout of the data because of data structures. It is like a template or a map. Suppose we want to store an address, it has two parts: number and string. When we define how many bytes will be the number and how many for the string, it is a data structure. When we store this address it will start on a word offset. We can also define a flag as a data structure, which gives true or false.

Hard Disk Technology Format Tracks and sectors. Sectors are typically 512 bytes. Each sector is given an address starting with 1 for each track. Tracks starts with 0. Since we have two sides to each disk and many disks, they are numbered known as head number. The tracks are referred to as cylinder. So we need head, Cylinder and Sector to get to a particular sector on a hard drive; this is CHS addressing. CHS addressing is too limited because too few bits were allowed for addressing, maximum size supported was 504 MB. A work around was for BIOS to do an intermediate calculation. This expanded the size to 8.1GB. Now we use the LBA addressing (logical block addressing). This addressing starts with 1 and goes up. To convert to LBA use this: –LBA=(((cylinder * heads/cyl)+head)*sectors/track+sector-1 ATA/IDE – Master/Slave/CS configuration

Protection Hard disk passwords ATA-3 spec. –BIOS can assign master and user passwords –Host protected area. A special area of the disk that can be used to save some system information added there by the manufacturer, say drivers. –Device configuration overlay. ATA-4 spec. Data can be hidden using this.

Other Info Serial ATA. ATA-7 spec. Only has 7 contacts. No chaining of multiple devices. Direct Access to controller. Two ways to access ATA hard drives: through BIOS and Direct Access: –To access through BIOS the software must load data such as the sector address and sizes into the CPU registers and execute interrupt 13h –Direct access requires software to know how to address the controller and how to issue commands to it. SCSI –8 bit - SCSI 5MB/s, Fast SCSI 10MB/s, Ultra SCI 20MB/s, Ultra2 SCSI 40 MB/s all gave twice rate with 16 bit transfer. Ultra 3 SCSI 160MB/s, Ultra320 SCSI 320 MB/s (only in 16 or higher bits).