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��Դ��Фس��ѵԢͧ˹��红��ͧ

�ػ�ó�ѹ�֡�� (storage device) ��͢�� С�䡡�úѹ�֡��¡��ŷ��ѹ�֡��ͫ��Ѻ��ҹ��ͺѹ�֡��͢��

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��Դ��Фس��ѵԢͧ˹��红��ͧ
1 ��͢��
�س��ѵ��ػ�ó�ѹ�֡��¹͡
2 ෻��
��ʹ��Т�ͨӡѴ㹡��෻��
3 �ҹ��
�ѡɳзҧ��Ҿ
��ʹ��Т��¢ͧ��ҹ��

1 ��͢��

��ѵ�طҧ��Ҿ��纺ѹ�֡��ٻ��᷹�� 2 ��Դ��

1. Volatile ��ŷ��ѹ�֡��ա��俿�Ҽ�ҹ �� RAM �ͧ˹��¤��ѡ

2. Nonvolatile ��Ŷ١�ѹ�֡��ҧ��ź�� ա��俿�� ROM �ѵ�� ͢��ŷ��ö�红��ҹ��

��ҧ��Ͱҹ��Ũе�ͧ��ѡ��͡��ͺѹ�֡��е�ͧ�ӹ֧�֧�к��ŷ��ػ�ó�ѹ�֡��§� ��෻��Ҷ֧��੾��Ẻ�ӴѺ 㹢�з��ҹ��ػ�ó�ѹ�֡��ŷ��Ҷ֧�µç��ҧ��͢��ŷ��Ҷ֧Ẻ�ӴѺ��鹷�� ੾�С��¹��Ѵ价��з�� 㹢�з��͢��Ҷ֧Ẻ�� ö��˹��ô��㹡�á�˹��˹��š��Ҷ֧ ��ǹ�ͧ��ͺѹ�֡��ö��˹��˹��

�س��ѵ��ػ�ó�ѹ�֡��¹͡
1. ��Ҷ֧��
(access time) �е�ͧ��Ǿͷ��з��û��żŢ��Ҿ�� 2. ��آͧ��红��
(storage capacity) ��ͧ�դ��ҡ��Ѻ��红��ŷ��ͧ��㹡�û��ż��ҧ��§�� 3. ��ʹ��
(security) ��ͺѹ�֡��ŵ�ͧ�դ��ҹ ��л�ʹ��¨ҡ��·��Դ�� ͹ �� 4. �ѵ�ҡ�ö��·ʹ��
(transfer rate) ��ҷ��㹡�ö��·ʹ��Ũҡ/��ҧ˹��¤��ӡѺ�ػ�ó��ͺѹ�֡��¹͡ ��ͧ�Ǵ�� 5. �Ҥ�
(cost) ��Ҥ�ᾧ��è��դ��٧㹡��Ҷ֧�� ·��Ҥҵ��˹��µ�ͧ��§�ͷ��л��Ѵ��¢ͧ�ҹ��к� 6. �ҵðҹ
(standardization) ��͡��ػ�ó�ѹ�֡��ŷ��ҵðҹ ��Ѻ��ͧ�� 7. �Ըա��Ҷ֧��
(access mode) ��èз��駡��Ҷ֧��Ẻ�ç (direct access) ��Ẻ�ӴѺ (sequential access) 8. ��Դ��дǡ
(portability) �բ�Ҵ��зѴ�Ѵ �ӵԴ��дǡ �� ෻�� ҹ��硷��öʹ�ҡ��ͧ�� 2 ෻��
(magnetic tape)

��ͺѹ�֡��ŷ��ѹ��ҧ��ҧ��ҧ��Ѻ��Ţ�Ҵ�˭� ��л��ż�Ẻặ�� (batch processing) ෻��ػ�ó�ѹ�֡��ŷ��Ҷ֧��Ẻ�ӴѺ�Ӥѭ��Դ˹�� ෻��硷Ӵ��þ��ʵԡ�Һ�� ·��仡��ҧ 0.5 �� ǻ��ҳ 2400-3600 �ص

��᷹��Ң��෻�� 2 �к� ��

1. �к� 7 ᶺ (7-track tape) ��Ѻ��ʢ��Ẻ�իմ� (BCD)

2. �к� 9 ᶺ (8-track tape) ��Ѻ��ʢ��Ẻ�ͺ�Դԡ (EBCDIC) �� ʡ� (ASCII)

Parity Check Bit
�繺Ե��ҡ�Ե�ͧ��ʢ�� 㹢�кѹ�֡��ŧ෻ ��Ѻ��Ǩ�ͺ��١��ͧ�ͧ��ҧ��ҹ��ź�෻ ��ҷ��ͧ�Ѻ෻��ҹ/�ѹ�֡��ź�෻ �е�ͧ��ͧ�դ��Ǿ�� ҹ/�ѹ�֡ (read/write head) �֧�зӧҹ�� ѧ��鹨ҡ��ͧ෻��Ҿ��觨��з��Ǿ��й��͹��ҹ��෻��ǹ˹�� ͻ�ͧ�ѹ��źҧ��ǹ�Ҵ�� ֧��ͧ��ͷ��ҧ��ҧ��¹��¡�� Inter Record Gap (IRG) ��բ�Ҵ��ǻ��ҳ 0.5 �� ֧ 0.75 �� ෻��ǹ˹��ǹ�� IRG ��٧�֧ 90% �ͧ��෻ �ѧ��鹶�Ҩӹǹ IRG ��ҡ��آͧ��෻��觹�� ѧ��鹨֧��Ըա�ú��͡ (block) ��͡��¹��ҧ��Ҵ��¡ѹ�繡��ͨ��ͷ��è��¹��ҡ�� ᷹��е�ͧ�� IRG ��蹷ء��¹��Ըա�ú��͡��Ǩ�� IRG ��ҧ��к��͡

��¹��ҧ��Ҵ��¡ѹ�繺��͡�� Ŵ�ӹǹ��駢ͧ��ö��·ʹ�� ֧�繡��㹡�÷ӧҹ�ͧ�� 㹢��ǡѹ��Է��Ҿ�ͧ��෻ ��෻�红��ҡ�� Ţ��ʴ��ӹǹ��¹��к��͡��¡�� blocking factor �դ��ҡ ��෻��ջ��Է��Ҿ ��ҧ�á��Ҵ�ͧ��͡�е�ͧ��Թ��Ҵ�ͧ�ѿ��˹��¤��

��ʹ��Т�ͨӡѴ㹡��෻��

��ʹ�

1. ��ӡѴ��Ǣͧ��¹��¹��鹨��դ��ǡ��ѡ�á�� ö�ѹ�֡ŧ�෻��дǡ

2. ��Ѵ��ͷ��㹡�èѴ��ѵ�Ҥ��˹��㹡�úѹ�֡�٧

3. �Ҥҵ��˹��¶١

4. ��㹡�ö��·ʹ��Ţͧ��ͧ෻��ҳ 40,000 ��ѡ�õ��Թҷ�

5. ��ͧ (backup file)

��ͨӡѴ

1. ��ö��ҹ��µ�� ͧ��ͧ��ҹ

2. ��Ҷ֧��ŷ��è��µç ��ͧ��ҹ��

3. ��żŢ��ŷ��੾��Ẻ�ӴѺ (sequential processing)

4. �Ѩ��·ҧ��ҹ��Ҿ�Ǵ�� ͹ �� س��ռŵ�͢��ŷ��ѹ�֡�෻

5. ��ö��Ҷ֧��§�� 1 ��ҹ��

3 �ҹ��
(magnetic disk)

��ػ�ó�ѹ�֡��ŷ��ö��Ҷ֧��µç (direct access storage device) ��Դ˹�觷��ѹ��ҧ��ҧ��ҧ ��з��к��ҹ�դ��ͧ��㹡��͡Ẻ�ҹ �շҧ��͡�ҡ�� Ҩ��繧ҹ�͹�Ź�, ��ͺ�� ͡�û��ż�Ẻặ��

�ѡɳзҧ��Ҿ

�蹨ҹ��硩Һ��硷��ǧ��¡��ä (track) ��ҳ 200-800 �ä��ͼ�Ǩҹ ��˹��Ţ��äǧ�͡�ش��ҡѺ 0 �ä�Ѵ��ҡѺ 1 ��ӴѺ�� ǧ��ش��Ţ��ҡѺ 199 (��Ѻ�蹨ҹ�� 200 �ä) ��Ѻ�ҧ�к� �Ҩ��ä�͡��˹��·��ŧ��ա��¡ ૡ�� (sector) ��˹��红��ŷ��硷��ش��ҹ��ö��˹��˹觷�� »��Ԥ��آͧ��ૡ��Ѻ��ѷ��Ե�Ҩ�� 128 亵� �� 256 亵��ૡ��

�ҹ��ҧ��͹�ѹ��¡��Ҫش�ҹ�� ·��蹨ҹ�ء��ҹ��ըӹǹ�ä��ҡѹ ��Ţ��͹�ѹ ��ö�ѹ�֡��ź��ҹ��ͧ�ͧ�蹨ҹ ¡��鹴�ҹ��ش��д�ҹ��ҧ�ش�ͧ�ش�ҹ�� ǹ��١�� 蹨ҹ�ͧ�ش�ҹ�� 10 �� кѹ�֡��§ 18 ��ҹ��ҹ��

Cylinder ��͡��ͧ�ä��Ţ��ǡѹ �ش�ҹ��Ъش�ըӹǹ cylinder ��ҡѺ�ӹǹ�ä �� cylinder ��ըӹǹ�ä��ҡѺ�ӹǹ��ҹ��ѹ�֡�� úѹ�֡��ŵ�� cylinder ��Ҷ��·ʹ��Ź��¡�� ͧ�ҡ��ͧ��͹��ҹ/�ѹ�֡��

��ͧ�Ѻ�ҹ��ª�Դ �ѧ��

1. ��ͧ�Ѻ�ҹẺ��ҹ��Ѻ�� (fixed head disk drive) �繪�Դ��蹨ҹ�Դ��Ѻ��ͧ ��ҹ/�ѹ�֡�ء��ä �� seek time �ѧ��鹨֧�դ��㹡�ö��·ʹ��٧�ҡ ��Ѻ�纫Ϳ��к��ҹ��ͧ��ä��Ǵ��

2. ��ͧ�Ѻ�ҹẺ��ҹ��͹�� (moving head disk drive) ��Դ��ҹ/�ѹ�֡ 1 �ش��ͼ�Ǩҹ 1 ��ҹ �ҤҶ١��Ẻ�á ��ö��蹨ҹ��͡�ҡ��ͧ�� Ѻ�纫Ϳ��ء��Т��ŷ��

3. ��ͧ�Ѻ�ҹẺ�Թ�� (winchester disk drive) ��෤�� ҹ��դ��ա 6-10 ��Ф��㹡�÷ӧҹ�� ҹ��硷��෤��ըж١��Դ��㹵��ͧ��͡��ѡ��Ҵ��ʹ�� 蹨ҹ�Ӵ��Һ�� ferric oxide

��ͧ�ҡ��˹��㹡�úѹ�֡��Ũҹ��硢��Ѻ��ҧ��ҧ��ҹ/�ѹ�֡�Ѻ��Ǩҹ ��ҧ��觹��¤��ب��ҡ �͡�ҡ��ҹ��硷�� ѡ�л��ʺ�ѭ��ҹ/�ѹ�֡��ᷡ��Ǩҹ ��źҧ��ǹ�٭��ͷ��蹨ҹ�� ͧẺ��ҹ/�ѹ�֡��չ��˹ѡ��

��ҷ��㹡��ҹ/�ѹ�֡�� (access time) ��ҹ��硢��Ѻ

1. ��

(seek time) ��ҷ�� head assembly ��觤��ǻ��Լ�ҹ cylinder ��ҧ��ѧ cylinder ��ͧ�� Ŵ��ŧ��ش�� ҹ��Ѻ��ҧ��˹觻Ѩ�غѹ�ͧ��ҹ/�ѹ�֡�Ѻ��˹觢ͧ cylinder ��ͧ�� 2. ��͡��ҹ/�ѹ�֡
(R/W head selection) �� head assembly ��ѧ cylinder ��ͧ�� ͧ��͡��ҹ/�ѹ�֡��ä��ͧ��ë��͡��ҡ 㹡óշ��蹨ҹ��§�� ͧ��㹡��͡ 3. ��Ҫ�Ңͧ��ع
(rotation delay) ��ҷ��ŷ��ͧ��¹��㹵��˹觢ͧ��ҹ/�ѹ�֡ ��ҡѺ��˹�觢ͧ��ع 1 �ͺ 4. �ѵ�ҡ�ö��·ʹ��
(transfer rate) ��Ҷ��·ʹ��Ũҡ�蹨ҹ��ѧ˹��¤��Ӣ��Ѻ��˹��蹢ͧ��úѹ�֡��, ��㹡��ع��Ф��Ǣͧ��¹

��ҡ��Ҷ֧�ͧ�ҹ��ö�ӹǳ��ѧ��

access time
= �� (seek time) + ��ҷ��㹡��͡��ҹ/�ѹ�֡ (R/W head selection time) + ��Ңͧ��Ҫ�Ңͧ��ع (rotation delay time) + ��㹡�ö��·ʹ�� (transfer time)

��ҧ

��äӹǳ��ҷ��㹡��ҹ/�ѹ�֡ �� ˹�� seek time 60.0 ms. Rotation time 12.5 ms. Transfer rate 250 ��ѡ��/ms.

��Ң��ŷ��ҹ�� 1000 ��ѡ�� ҷ��ҡѺ

seek time 60.0 ms.

Rotation time 12.5 ms.

Read 4.0 ms. (�ӹǳ�ҡ transfer rate 1000/250 = 4 ms.)

��ҷ��㹡��ҹ�� 76.5 ms.

��繡�� update ��㹡�úѹ�֡��˹��ҡѺ

seek time 0.0 ms. (��ͧ�� cylinder)

Rotation time 12.5 ms.