Loved Ginny Tom Riddle

How did Tom Riddle get his memories into the diary?

It has nothing to do with Pensieve. The confusion arises because Voldemort is the one who describes the diary as a book of memories. Voldemort was of course very secret about his Horcruxes and would never call a Horcrux as it really is under any circumstances. Consequently, Riddle describes the diary as a memory bank. It was actually a watchful and living soul piece, who had access to Lord Voldemort's memory and life experiences when the Horcrux was created. Kevin makes this point, but I thought I'd add a longer answer to explain why this is exactly the case.

We see from the medallion in Deathly Hallows, that soul pieces in Horcruxes are not sleeping, static objects waiting silently in the camp. Rather, they are living and listening spirits who respond to what is happening around them.

Ron passed the Horcrux on to Harry. After a moment or two, Harry thought he knew what Ron was talking about. Was it his own blood pulsing through his veins that he could feel, or was something beating in the locket like a tiny metal heart?
(Deathly Hallows, Chapter 14, The Thief) .

Harry noticed the locket on his skin; the thing in it that was ticking or beating sometimes had woken up; he could feel it pulsing through the cold gold. Did it know, could it feel that the thing it was going to destroy was nearby?
(Deathly Hallows, Chapter 17, Bathilda's Secret) .

Then something tightened around his neck. He thought of aquatic weeds, although nothing brushed him while diving, and raised his empty hand to free himself. It wasn't a weed: the Horcrux's chain had tightened, slowly narrowing its windpipe.
(Deathly Hallows, Chapter 19, The Silver Doe) .

The soul piece in the Horcrux is audible, beats faster when excited and can even attempt executions. The Medallion Horcrux recreates the character and personality of the man whose soul it contains. Voldemort is cruel and manipulative, and hence the locket.

Then a voice hissed from the Horcrux.
" I've seen your heart and it's mine. "
"Do not listen!" Harry said harshly. "Prick it!"
" I've seen your dreams, Ronald Weasley, and I've seen your fears. Anything you wish is possible, but anything you fear is also possible ... "
"Sting!" yelled Harry; His voice echoed from the surrounding trees, the tip of the sword trembled and Ron looked into Riddle's eyes.
" Least loved, always by the mother who longed for a daughter ... least loved, now by the girl your girlfriend favors ... second best, always, forever overshadowed ... "
(Deathly Hallows, Chapter 19, The Silver Doe) .

The locket speaks in Riddle's voice and contains Riddle's eye because it contains a piece of riddle. During this scene, it proves its sensation. It speaks, it channels Harry and Hermione, and it even bursts out of the confines of its object to become a physical appearance.

Out of the locket's two windows, out of sight, the heads of Harry and Hermione bloomed like two grotesque bubbles, strangely contorted.
Ron screamed in shock and backed away as the figures from the locket blossomed, first chest, then waist, then legs, until they stood in the locket, side by side like trees with a common root ...
(Deathly Hallows, Chapter 19, The Silver Doe) .

In other words, the medallion puzzle behaves and behaves remarkably like the diary puzzle. In either case, neither of them are accurate memories . Both are fragments of the soul. They live, they wait, they hunt and - when powerful enough and circumstances permit - they speak and break out of the confines of their Horcrux. The trigger for this in the case of the locket was that Harry opened the locket through Parseltongue. The trigger in the case of the diary was that Ginny poured enough of her soul into the diary that Riddle was strong enough to leave it.

"But there is not much life left in her: she has put too much into the diary, into me. Enough to finally let me leave his pages."
(Chamber of Secrets, chapter 17, The Heir of Slytherin) .

The skills that had to write back diary puzzles, forcing, tricking, lying, pressuring and stepping out of the diary came from his nature as a soul fragment. The magic that drove him was the magic of the Horcruxes, not spells related to memory, pensieve, or any other branch of magic. Riddle says this directly: It was him self which he wrote in the diary, no magic.

"I decided to leave a diary and my sixteen year old self to keep on his pages so that one day, with a little luck, I could follow in my footsteps and finish Salazar Slytherin's famous work. "
(Chamber of Secrets, chapter 17, The Heir of Slytherin) .

Notice that he says he wrote his "self" in the journal, not just his memories.

It is the sixteen-year-old riddle that lives in the diary, and so this particular soul fragment contained the memories of the sixteen-year-old riddle. As a result, he can include Harry in his memory of Hagrid's capture. However, it is far more than the memory that is in the diary. It is Voldemort himself . This applies to all horcruxes.

Does that mean that the diary was no different from any other Horcrux back then? No. As the question rightly suggests, the diary was different in that it was a weapon, not just a soul container.

"What intrigued and worried me most was that the diary was intended as both a weapon and protection."
"I still don't understand," said Harry.
"Well, it worked the way a Horcrux is supposed to work - in other words, the soul fragment hidden inside was kept safe and had undoubtedly helped prevent the death of its owner. But there could be no doubt that Riddle really wanted it This diary read, wanted the piece of soul to inhabit or possess someone so that Slytherin's monster could be unleashed again. "
(Half-Blood Prince, chapter 23, Horcruxes) .

The nature of the diary meant that it could possess people and communicate with people in ways that the other Horcruxes could not.

As I said earlier, the diary was no different in its ability to be sentient, to speak, to force, or to break free from the confines of its object. All Horcruxes could do this under the right circumstances. The diary should not only be read, but also interacted with. A diary is as interactive as a medallion, ring, tiara, snake, and cup really aren't. This meant that it not only fed on the negativity and discomfort of those around it, as the locket did; it has also destroyed the souls of those who wrote in it and weakened them so that possession is possible.

"So Ginny poured out her soul to me and her soul was exactly what I wanted. I was getting stronger and stronger on a diet of her deepest fears, her darkest secrets. I became more powerful, much more powerful than little Miss Weasley. Powerful enough to Miss Weasley a couple mine Feed secrets and a little of mine Soul back in you to pour ... "
(Chamber of Secrets, chapter 17, The Heir of Slytherin) .

It is the uniqueness of the diary as a means of opening the Chamber of Secrets and as a method of communication that enables possession that separates it from the other Horcruxes. It is important to understand this distinction to see that it wasn't additional, unknown magic that gave diary puzzles the powers it had. He was a horcrux like any other. But because the object in which it was placed was a diary, unlike the other Horcruxes, it could stain the souls of everyone who wrote in it. But his memories, his nature, and the magic that sustained him were Horcrux magic, just like the other Horcruxes.

In summary, the "more durable than ink" method Riddle used to preserve his memories was through creating horcruxes.Riddle not only wrote his memories in the journal, he poured himself.The soul fragment in the diary appeared to be autonomous like all the others.And it had access to Riddle's memories, like everyone else.The diary could be owned by people while the others couldn't because it was not meant to be owned.But in every other way the diary and the other Horcruxes were exactly the same.

amflare

As well as this answer is to explain how the diary works, the OP does not answer it. Special "How did Tom Riddle fill the diary with his own memories?" . Or did I miss it? If not, can you add it?

The dark lord

@amflare The memories went in next to the soul fragment when the Horcrux was made. Hopefully the title and last paragraph make this clear, although I got carried away with a little detail in the middle so maybe my point was lost.